1. Field of the Invention
The present invention pertains to an optical sensing system for detecting moving objects. The sensing system may be used in any suitable application, including intrusion alarm systems, factory process monitors, vending machine dispensing sensors, and similar systems that require reliably sensing objects passing through a volume of interest. Although the invention may be used in any suitable application, for simplicity it will be described herein as used with a vending machine to detect whether an object has been properly vended.
2. Description of Related Art
In a typical vending machine, there is stored an array of articles ranging from small to large. Some vending machines contain relatively small objects such as metal screws, metal washers, or candy while other vending machines contain relatively large objects such as cans of soda and bags of snack foods. When a user makes the requisite payment or enters the proper access code to the machine and makes a desired selection on the selector panel, the selected product is released from its storage position by one of many known electromechanical mechanisms. It then tumbles downward, drawn by gravity, through a vend space between the front of the vend mechanisms and the back of the machine's front panel, into an outlet bin, from which the user can retrieve it. In many vending machines the machine's front panel is transparent thereby allowing the user to view the products before making a selection.
Several different problems may occur during the vending operation. For example, the vended product may get stuck in the machine before delivery to the user. Alternatively, the machine may dispense too many products to the user. Spatial orientation of packages and wrinkling of packaging, unusual random distribution of contents of a package, unusual random tumbling of a package through the vend space, an empty pocket in a dispensing mechanism, mis-feed of the dispensing mechanism, multi-feeds, and similar events all can cause mis-vending. In any case, certain actions need to be taken to provide a refund to the user, allow the opportunity to make another selection, or alert the machine owner that improper vending has occurred.
The physical characteristics of products dispensed from vending machines may vary widely. The products size may vary in volume and shape, typified by such product extremes as metalized plastic bags of snack food (typically 5×8×2 inches), thin paper cards (typically 3×5×0.060 inches), beverage cans (typically 6×2.5 diameter, inches), machine screws (1×0.125 diameter, inches), gum packages (typically 0.625×1.25×2.5 inches), and machine nuts (typically 0.125×0.125×0.040 inches). Such typical products may randomly tumble in three dimensions, such that the profile presented along any axis during the dispensing process may vary from the thinnest dimension to the widest dimension.
It is known in the art to provide an emitter and detector which provide a beam in a confined space through which the vended product will fall. A processor determines when a vended product breaks the beam to confirm that the product has been vended properly. In prior art devices, however, there is some chance that the falling product, through random orientation will fail to break the beam, or will apparently fail to break the beam, and therefore not be detected. There is also a possibility that in constricting the space through which the product must fall, random orientation will cause the product to bridge and become lodged in the constricted space, having been detected but not having been successfully vended.
Others have provided vend sensors in which the impact on the outlet chute of a comparatively heavy vended article such as a can or bottle, is sensed as a vibration. However, such sensing is not economically feasible where at least some of the products being vended are very light in weight, such as is the case where a small number of large potato chips are presented in a facially large but light in weight package made of synthetic plastic film.
A particularly difficult situation is presented when some of the products to be dispensed are large so that a large transverse cross-sectional area is required for the vend space, but others of the products are so small that an optical beam meant to be broken by the product could be missed due to random path of movement and changing spatial orientation of the falling product being vended.
There is therefore a need for an improved sensing system which overcomes these and other deficiencies in the prior art.